Imaging optical system

ABSTRACT

“f” designates the overall focal length; f1, R1 and D1 respectively designate the focal length, paraxial radius of curvature of an object-side surface, and thickness, of the negative lens element closest to the object; and V designates the Abbe number regarding the d-line of a lens element, within the second lens group, closest to the diaphragm.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.15/450,456, filed Mar. 6, 2017, which claims the benefit of JapanesePatent Application No. 2016-052422, filed on Mar. 16, 2016. The entiredisclosure of each of the above-identified applications, including thespecification, drawings, and claims, is incorporated herein by referencein its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an imaging optical system which can beprovided in an imaging apparatus such as, e.g., an in-vehicle camera, asurveillance camera, and a portable terminal (including a mobile phone,a smart phone or other smart devices).

2. Description of Related Art

An imaging optical system is known in the related art that can achieveboth a wide angle-of-view and a higher definition of a telescopic imagein a central area of a picture frame. Patent Literature 1 discloses animaging optical system which achieves a wide angle-of-view by causing alarge amount of negative distortion, and achieves an enlarged (anddistorted) image in the central area of the picture frame.

Patent Literature 1: Japanese Unexamined Patent Publication No.2005-010521.

However, in the imaging optical system of Patent Literature 1, theoverall length of the imaging optical system becomes long when set to alarge aperture; and if the overall length of the imaging optical systemis shortened, there is the disadvantage of not being able to provide alarge aperture ratio. For example, the fourth embodiment in PatentLiterature 1 discloses an imaging optical system having a relativelylarge aperture having an f-number of about 1.8. However, the value ofthe overall length of the imaging optical system divided by the maximumimage height is 9.8; hence, the overall length of the imaging opticalsystem is long relative to the maximum image height. Whereas, in thefirst embodiment of Patent Literature 1, the value of the overall lengthof the imaging optical system divided by the maximum image height is5.1, so that the overall length of the imaging optical system is shortrelative to the maximum image height; however, the f-number is 2.8,i.e., the aperture ratio is not very large.

SUMMARY OF THE INVENTION

The present invention has been devised in view of the above-describedproblems, and provides an imaging optical system which can achieve awide angle-of-view while enlarging the object image at the central areaof the picture screen, has a short overall length, has a large aperture,and various aberrations can be favorably corrected.

According to an aspect of the present invention, an imaging opticalsystem is provided, including a positive or negative first lens group,an aperture diaphragm, and a positive second lens group, in that orderfrom the object side. The first lens group includes a negative lenselement provided closest to the object side within the first lens group.The negative lens element that is closest to the object side includes anaspherical surface on the object side thereof, the aspherical surfaceincluding a paraxial convex surface convexing toward the object side, aparaxial curvature (curvature of the central portion) that is thegreatest within the effective aperture, and a portion within theeffective aperture that has a curvature that is less than ½ of theparaxial curvature (curvature of the central portion). The followingconditions (1), (2), (3) and (4) are satisfied:

R1/f<1.35  (1),

D1/f>0.4  (2),

−2.5<f1/f<−1.3  (3), and

V>56  (4),

wherein f designates the focal length of the imaging optical system, f1designates the focal length of the negative lens element providedclosest to the object side within the first lens group, R1 designates aparaxial radius of curvature of a surface on the object side (the radiusof curvature of the paraxial convex surface) of the negative lenselement provided closest to the object side within the first lens group,D1 designates a thickness, along the optical axis, of the negative lenselement provided closest to the object side within the first lens group,and V designates the Abbe number with respect to the d-line of a lenselement, within the second lens group, that is provided closest to theaperture diaphragm.

It is desirable for the following condition (4′) to be satisfied withinthe scope of condition (4):

V>63  (4′).

In the present specification, in addition to the case where an aperturediaphragm is positioned between a surface closest to the image side onthe first lens group and a surface closest to the object side on thesecond lens group, “a first lens group, an aperture diaphragm and asecond lens group, in that order from the object side (in other words,an aperture diaphragm is provided between the first lens group and thesecond lens group)” also refers to the case where the aperture diaphragmis positioned on a plane that is orthogonal to the optical axis and istangent to surface closest to the image side on the first lens group, orat a position that is slightly toward the object side from such a planeso that the aperture diaphragm and the first lens group overlap withrespect to the optical axis direction; and also refers to the case wherethe aperture diaphragm is positioned on a plane that is orthogonal tothe optical axis and is tangent to surface closest to the object side onthe second lens group, or at a position that is slightly toward theimage side from such a plane so that the aperture diaphragm and thesecond lens group overlap with respect to the optical axis direction.

In the present specification, “effective aperture of a lens element”refers to the maximum area of a light-ray passage of the lens elementdetermined by light rays that pass through the lens element at a maximumposition (distance) from the optical axis out of the light rays from thecenter (on the optical axis) of an image, formed by an optical systemthat includes the lens element, to the maximum image height.

It is desirable for the following condition (5) to be satisfied:

−0.45<f1/fg1<1  (5),

wherein f1 designates the focal length of the negative lens elementprovided closest to the object side within the first lens group, and fg1designates the focal length of the first lens group.

It is desirable for the following condition (6) to be satisfied:

0.3<(R1−R2)/(R1+R2)<0.55  (6),

wherein R1 designates the paraxial radius of curvature of the surface onthe object side (the radius of curvature of the paraxial convex surface)of the negative lens element provided closest to the object side withinthe first lens group, and R2 designates the paraxial radius of curvatureof the surface on the image side of the negative lens element providedclosest to the object side within the first lens group.

It is desirable for the first lens group to include a positive lenselement behind the negative lens element provided closest to the objectside within the first lens group.

It is desirable for the positive lens element that is provided behindthe negative lens element provided closest to the object side, withinthe first lens group, to be a positive meniscus lens element having aconvex surface on the image side.

It is desirable for the positive lens element that is provided behindthe negative lens element provided closest to the object side, withinthe first lens group, to have an Abbe number of at least 35 with respectto the d-line.

It is desirable for the second lens group to include at least onepositive lens element that has an Abbe number of at least 70 withrespect to the d-line.

It is desirable for the second lens group to include at least onenegative lens element that has an Abbe number of 20 or less with respectto the d-line.

According to the present invention, an imaging optical system isobtained, which can achieve a wide angle-of-view while enlarging theobject image at the central area of the picture screen, has a shortoverall length, has a large aperture, and various aberrations can befavorably corrected.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 2016-052422 (filed on Mar. 16, 2016) which isexpressly incorporated herein in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be discussed below in detail with referenceto the accompanying drawings, in which:

FIG. 1 shows a lens arrangement of a first numerical embodiment of animaging optical system, according to the present invention;

FIGS. 2A, 2B, 2C and 2D show various aberrations that occurred in thelens arrangement of FIG. 1;

FIG. 3 shows a lens arrangement of a second numerical embodiment of animaging optical system, according to the present invention;

FIGS. 4A, 4B, 4C and 4D show various aberrations that occurred in thelens arrangement of FIG. 3;

FIG. 5 shows a lens arrangement of a third numerical embodiment of animaging optical system, according to the present invention;

FIGS. 6A, 6B, 6C and 6D show various aberrations that occurred in thelens arrangement of FIG. 5;

FIG. 7 shows a lens arrangement of a fourth numerical embodiment of animaging optical system, according to the present invention;

FIGS. 8A, 8B, 8C and 8D show various aberrations that occurred in thelens arrangement of FIG. 7;

FIG. 9 shows a lens arrangement of a fifth numerical embodiment of animaging optical system, according to the present invention;

FIGS. 10A, 10B, 10C and 10D show various aberrations that occurred inthe lens arrangement of FIG. 9;

FIG. 11 shows a lens arrangement of a sixth numerical embodiment of animaging optical system, according to the present invention;

FIGS. 12A, 12B, 12C and 12D show various aberrations that occurred inthe lens arrangement of FIG. 11;

FIG. 13 shows a lens arrangement of a seventh numerical embodiment of animaging optical system, according to the present invention;

FIGS. 14A, 14B, 14C and 14D show various aberrations that occurred inthe lens arrangement of FIG. 13;

FIG. 15 shows a lens arrangement of an eighth numerical embodiment of animaging optical system, according to the present invention;

FIGS. 16A, 16B, 16C and 16D show various aberrations that occurred inthe lens arrangement of FIG. 15;

FIG. 17 shows a lens arrangement of a ninth numerical embodiment of animaging optical system, according to the present invention;

FIGS. 18A, 18B, 18C and 18D show various aberrations that occurred inthe lens arrangement of FIG. 17;

FIG. 19 shows a lens arrangement of a tenth numerical embodiment of animaging optical system, according to the present invention;

FIGS. 20A, 20B, 20C and 20D show various aberrations that occurred inthe lens arrangement of FIG. 19;

FIG. 21 shows a lens arrangement of an eleventh numerical embodiment ofan imaging optical system, according to the present invention;

FIGS. 22A, 22B, 22C and 22D show various aberrations that occurred inthe lens arrangement of FIG. 21;

FIG. 23 shows a lens arrangement of a twelfth numerical embodiment of animaging optical system, according to the present invention;

FIGS. 24A, 24B, 24C and 24D show various aberrations that occurred inthe lens arrangement of FIG. 23;

FIG. 25 shows a lens arrangement of a thirteenth numerical embodiment ofan imaging optical system, according to the present invention; and

FIGS. 26A, 26B, 26C and 26D show various aberrations that occurred inthe lens arrangement of FIG. 25.

DESCRIPTION OF THE EMBODIMENTS

The imaging optical system of the present invention is configured of apositive or negative first lens group G1, an aperture diaphragm S, and apositive second lens group G2, in that order from the object side. Ineach of the first and fifth numerical embodiments, the first lens groupG1 has a positive refractive power. In each of the second through fourthand sixth through thirteenth numerical embodiments, the first lens groupG1 has a negative refractive power. In each of the first, second,fourth, fifth and seventh through thirteenth numerical embodiments, acover glass CG is provided between the second lens group G2 and animaging surface IM. In each of the third and sixth numericalembodiments, an optical filter OP and a cover glass CG are providedbetween the second lens group G2 and the imaging surface IM.

In the first numerical embodiment, the first lens group G1 is configuredof a negative lens element 11 formed from aspherical glass molded lenselement (having an aspherical surface on each side thereof), and apositive lens element 12 formed from a spherical glass lens element, inthat order from the object side. The aspherical surface on the objectside of the negative lens element 11 includes a paraxial convex surfaceconvexing toward the object side, a paraxial curvature (curvature of thecentral portion) that is the greatest within the effective aperture, anda portion within the effective aperture (at a peripheral portion otherthan the paraxial portion) that has a curvature that is less than ½ ofthe paraxial curvature (curvature of the central portion). The positivelens element 12 is a biconvex positive lens element.

In each of the second through fourth and sixth through thirteenthnumerical embodiments, the first lens group G1 is configured of anegative lens element 11 formed from an aspherical glass molded lenselement (having an aspherical surface on each side thereof), and apositive lens element 12 formed from aspherical glass molded lenselement (having an aspherical surface on each side thereof), in thatorder from the object side. The aspherical surface on the object side ofthe negative lens element 11 includes a paraxial convex surfaceconvexing toward the object side, a paraxial curvature (curvature of thecentral portion) that is the greatest within the effective aperture, anda portion within the effective aperture (at a peripheral portion otherthan the paraxial portion) that has a curvature that is less than ½ ofthe paraxial curvature (curvature of the central portion). The positivelens element 12 is a positive meniscus lens element having a convexsurface on the image side.

In the fifth numerical embodiment, the first lens group G1 is configuredof a negative lens element 11′ formed from an aspherical glass moldedlens element (having an aspherical surface on each side thereof), apositive lens element 12′ formed from a spherical glass lens element, anegative lens element 13′ formed from a spherical glass lens element,and a positive lens element 14′ formed from a spherical glass lenselement, in that order from the object side. The aspherical surface onthe object side of the negative lens element 11′ includes a paraxialconvex surface convexing toward the object side, a paraxial curvature(curvature of the central portion) that is the greatest within theeffective aperture, and a portion within the effective aperture (at aperipheral portion other than the paraxial portion) that has a curvaturethat is less than ½ of the paraxial curvature (curvature of the centralportion). The positive lens element 12′ is a positive meniscus lenselement having a convex surface on the image side. The negative lenselement 13′ is a negative meniscus lens element having a convex surfaceon the image side. The positive lens element 14′ is a biconvex positivelens element.

By providing the positive lens element 12 or 12′ subsequently(immediately) behind the negative lens element 11 or 11′, which isclosest to the object side within the first lens group G1, the height oflight rays of an abaxial light bundle incident on the negative lenselement 11 or 11′ can be reduced, and the diameter of the negative lenselement 11 or 11′ can also be reduced. Furthermore, by forming thepositive lens element 12 or 12′ as a positive meniscus lens elementhaving a convex surface on the image side, a negative refractive powercan be provided on the surface on the object side of the positive lenselement 12 or 12′, so that astigmatism and distortion can be favorablycorrected. Furthermore, by setting the Abbe number with respect to thed-line of the positive lens element 12 or 12′ to 35 or more, lateralchromatic aberration can be favorably corrected.

As shown in the first through thirteenth numerical embodiments that aredescribed hereinafter, there is a certain degree of freedom in theconfiguration of the second lens group G2 in which a number ofvariations are possible.

Among such variations, it is desirable for the second lens group G2 toinclude at least one positive lens element having an Abbe number of atleast 70 with respect to the d-line and/or at least one negative lenselement having an Abbe number of 20 or less with respect to the d-line.By including a positive lens element using a low-dispersion glass havingan Abbe number of at least 70, with respect to the d-line, within thesecond lens group G2, axial chromatic aberration can be favorablycorrected. By including a negative lens element using a high-dispersionglass having an Abbe number of 20 or less, with respect to the d-line,within the second lens group G2, due to a synergistic effect of thepositive lens element using a low-dispersion glass and the negative lenselement using a high-dispersion glass, axial chromatic aberration can bemore favorably corrected. Furthermore, since the refractive index ofsuch a negative lens increases, the radius of curvature also increases,so that light-ray angle of incident on the image sensor can be madesmaller.

A positive lens element or a negative lens element may be providedclosest to the aperture diaphragm (S) side within the second lens groupG2. For example, in the first numerical embodiment (described in detaillater), a negative lens element (21) is provided closest to the aperturediaphragm (S) side within the second lens group G2, and in the secondthrough thirteenth numerical embodiments (described in detail later), apositive lens element (21′, 21″, 21A, 21B, 21C or 21D) is providedclosest to the aperture diaphragm (S) side within the second lens groupG2.

In the imaging optical system of the illustrated embodiments, byreducing the effective aperture of the negative lens element 11 or 11′that is provided closest to the object side within the first lens groupG1 and reducing the number of lens elements, the overall length of theimaging optical system can be shortened, and miniaturization of theimaging optical system, and consequently the imaging apparatus in whichthe imaging optical system is provided, can be achieved. Furthermore,the imaging optical system of the illustrated embodiments achieves anf-number (lens speed) of 1.6.

In the imaging optical system of the illustrated embodiments, in orderto achieve a wide angle-of-view while enlarging the object image at thecentral area of the picture screen, the focal length, which determinesthe magnification of the central area of the lens, is increased and awider angle-of-view is provided at the lens peripheral portion.

More specifically, the aspherical surface on the object side of thenegative lens element 11 or 11′, provided closest to the object sidewithin the first lens group G1, has a profile that includes a paraxialconvex surface convexing toward the object side, a paraxial curvature(curvature of the central portion) that is the greatest within theeffective aperture, and a portion within the effective aperture (at aperipheral portion other than the paraxial portion) that has a curvaturethat is less than ½ of the paraxial curvature (curvature of the centralportion). Accordingly, it is possible to generate negative distortion tothereby achieve a wide angle-of-view. The smaller the curvature of theabove-mentioned “portion” of the negative lens element 11 or 11′,provided closest to the object side within the first lens group G1 (inthe case where the curvature is a negative value, the greater theabsolute value of the negative curvature), the more advantageous thenegative lens element 11 or 11′ is for widening the angle-of-view. Forexample, the aspherical surface on the object side of the negative lenselement 11 or 11′ can have the greatest paraxial curvature (curvature ofthe central portion) within the effective aperture, and the curvaturefrom a central portion toward the peripheral portion can be decreasedand thereafter increased at an outermost peripheral portion.

Condition (1) specifies the ratio of the focal length of the entire lenssystem (imaging optical system) to the paraxial radius of curvature ofthe surface on the object side (the radius of curvature of the paraxialconvex surface) of the negative lens element 11 or 11′ that is providedclosest to the object side within the first lens group G1. By satisfyingcondition (1), since the position of the principle point becomes distantfrom the imaging surface (imaging plane) IM (since the lateralmagnification in regard to the optical system after the surface on theobject side of the negative lens element 11 or 11′ increases), theparaxial focal length of the entire optical system increases, so thatthe object image at a central portion (of the picture frame) can beenlarged.

If the upper limit of condition (1) is exceeded, it becomes difficult toform an enlarged object image at a central portion of the picture frame.

Condition (2) specifies the ratio of the focal length of the entire lenssystem (imaging optical system) to the thickness of the negative lenselement 11 or 11′, provided closest to the object side within the firstlens group G1, along the optical axis. By satisfying condition (2),since the position of the principle point becomes distant from theimaging surface (imaging plane) IM (since the lateral magnification inregard to the optical system after the surface on the object side of thenegative lens element 11 or 11′ increases), the paraxial focal length ofthe entire optical system increases, so that the object image at acentral portion (of the picture frame) can be enlarged.

If the lower limit of condition (2) is exceeded, it becomes difficult toform an enlarged object image at a central portion of the picture frame.

By satisfying conditions (1) and (2), the focal length, normalized bythe image-sensor size, of the imaging optical system of the illustratedembodiments can be increased to 1.6 mm through 1.7 mm, so that theobject image at a central portion (of the picture frame) can beenlarged.

Condition (3) specifies the ratio of the focal length of the entire lenssystem (imaging optical system) to the focal length of the negative lenselement 11 or 11′, provided closest to the object side within the firstlens group G1. By satisfying condition (3), the overall length of theentire lens system (imaging optical system) can be shortened and theobject image at a central portion (of the picture frame) can beenlarged.

If the upper limit of condition (3) is exceeded, the focal length of thenegative lens element 11 or 11′ becomes too short, so that the lateralmagnification of the optical system thereafter (the remaining lenselements within the first lens group G1 and the second lens group G2)must be increased, thereby increasing the overall length of the entirelens system (imaging optical system).

If the lower limit of condition (3) is exceeded, it becomes difficult toform an enlarged object image at a central portion of the picture frame.

Conditions (4) and (4′) specify the Abbe number with respect to thed-line of the lens element (21, 21′, 21″, 21A, 21B, 21C and 21D)provided closest to the aperture diaphragm S and within the second lensgroup G2. By satisfying condition (4), even if the refractive power ofthe lens element that bears most of the positive refractive power burden(within the second lens group G2) is increased, occurrence of axialchromatic aberration can be suppressed; therefore, an imaging opticalsystem can be achieved which has an increased positive refractive power,thereby shortening the overall length of the lens system while achievinga large aperture and favorably correcting aberrations. The f-number ofthe imaging optical system of the illustrated embodiments isapproximately 1.6, the value of the overall length of the imagingoptical system divided by the maximum image height is approximately 6.3through 9.9, and achieves a shortened overall length of the imagingoptical system while having a larger aperture than that disclosed in theaforementioned Patent Literature 1. These functional effects are moreprominent when condition (4′) is satisfied.

If the lower limit of condition (4) is exceeded, it becomes difficult toachieve an imaging optical system which can have a large aperture andfavorably correct various aberrations.

Condition (5) specifies the ratio of the focal length of the negativelens element 11 or 11′ that is provided closest to the object sidewithin the first lens group G1 to the focal length of the first lensgroup G1. By satisfying condition (5), the object image at a centralportion (of the picture frame) can be enlarged, astigmatism can befavorably corrected, and the overall length of the lens system (imagingoptical system) can be shortened.

If the specified range of condition (5) is exceeded, since therefractive power of the negative lens element 11 or 11′ becomes small(weak), the focal length of the overall lens system (imaging opticalsystem) becomes short, so that it becomes difficult to form an enlargedobject image at a central portion of the picture frame.

Condition (6) specifies the shape (shaping factor) of the negative lenselement 11 or 11′ that is provided closest to the object side within thefirst lens group G1. By satisfying condition (6), the lens diameter ofthe negative lens element 11 or 11′ can be reduced, the overall lengthof the lens system (imaging optical system) can be reduced, and anenlarged object image at a central portion can be formed over a widerange within the picture frame.

If the upper limit of condition (6) is exceeded, the lens diameter ofthe negative lens element 11 or 11′ increases and the overall length ofthe lens system (imaging optical system) increases, so that it becomesdifficult to form an enlarged object image at a central portion of thepicture frame.

If the lower limit of condition (6) is exceeded, it becomes difficult tocorrect various aberrations.

NUMERICAL EMBODIMENTS

Specific numerical first through thirteenth embodiments will be hereindiscussed. In the aberration diagrams and the tables, the d-line, g-lineand C-line show aberrations at their respective wave-lengths; Sdesignates the sagittal image, M designates the meridional image, fdesignates the focal length of the entire optical system, Fno.designates the f-number, W designates the half angle of view (°), Ydesignates the image height (maximum image height), r designates the(paraxial) radius of curvature, d designates the lens thickness ordistance between lenses, N(d) designates the refractive index at thed-line, and νd designates the Abbe number with respect to the d-line.The unit used for the various lengths is defined in millimeters (mm).The “Effective Aperture” in the lens data indicates a radius (a distancefrom the optical axis).

An aspherical surface which is rotationally symmetrical about theoptical axis is defined as:

x=cy ²/(1+[1−{1+K}c ² y ²]^(1/2))+A4y ⁴ +A6y ⁶ +A8y ⁸ +A10y ¹⁰ +A12y ¹². . .

wherein ‘c’ designates the curvature (1/r) of the aspherical vertex, ‘y’designates the distance from the optical axis, ‘K’ designates the coniccoefficient, A4 designates a fourth-order aspherical coefficient, A6designates a sixth-order aspherical coefficient, A8 designates aneighth-order aspherical coefficient, A10 designates a tenth-orderaspherical coefficient, A12 designates a twelfth-order asphericalcoefficient, and ‘x’ designates the amount of sag.

Numerical Embodiment 1

FIGS. 1 through 2D and Tables 1 through 4 show a first numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 1 shows a lens arrangement of the imaging opticalsystem. FIGS. 2A, 2B, 2C and 2D show various aberrations that occurredin the zoom lens system of FIG. 1. Table 1 indicates the surface data,Table 2 indicates various lens system data, Table 3 indicates focallength data, and Table 4 indicates aspherical surface data.

The imaging optical system of the first numerical embodiment isconfigured of a positive first lens group G1, an aperture diaphragm S,and a positive second lens group G2, in that order from the object side.A cover glass CG is provided between the second lens group G2 and animaging surface IM.

The first lens group G1 is configured of a negative lens element 11formed from an aspherical glass molded lens element (having anaspherical surface on each side thereof), and a positive lens element 12formed from a spherical glass lens element, in that order from theobject side. The aspherical surface on the object side of the negativelens element 11 includes a paraxial convex surface convexing toward theobject side, a paraxial curvature (curvature of the central portion)that is the greatest within the effective aperture, and a portion withinthe effective aperture (at a peripheral portion other than the paraxialportion) that has a curvature that is less than ½ of the paraxialcurvature (curvature of the central portion). The positive lens element12 is a biconvex positive lens element.

The second lens group G2 is configured of a negative lens element 21formed from a spherical glass lens element, a positive lens element 22formed from a spherical glass lens element, and a positive lens element23 formed from an aspherical glass molded lens element (having anaspherical surface on each side thereof), in that order from the objectside. The negative lens element 21 is a negative meniscus lens elementhaving a convex surface on the object side, the positive lens element 22is a biconvex positive lens element, and the negative lens element(negative meniscus lens element) 21 and the positive lens element(biconvex positive lens element) 22 are cemented to each other. Thepositive lens element 23 is a positive meniscus lens element having aconvex surface on the object side.

TABLE 1 SURFACE DATA Effective Surf. No. r d N(d) νd Aperture  1* 6.9684.936 1.58313 59.5 6.77  2* 2.206 4.352 3.86  3 16.598 3.900 1.8348142.7 3.62  4 −19.444 0.788 3.07  5 (Diaphragm) ∞ 2.834 2.55  6 8.7511.000 1.94595 18.0 3.27  7 5.386 3.800 1.55032 75.5 3.30  8 −12.9230.889 3.83  9 6.749 2.500 1.55332 71.7 4.58 10* 14.838 3.055 4.21 11* ∞1.900 1.51680 64.2 4.03 12 ∞ 0.045 3.93 IM(Imaging Surface) The asterisk(*) designates an aspherical surface which is rotationally symmetricalwith respect to the optical axis.

TABLE 2 VARIOUS LENS SYSTEM DATA f 6.26 FNO. 1.66 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.14Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: −0.23 Focal lengthof entire optical system normalized by the image-sensor size: 1.64

TABLE 3 FOCAL LENGTH DATA Focal length of first lens group G1: 140.686Focal length of second lens group G2: 8.457 Focal length of negativelens element 11: −8.954 Focal length of positive lens element 12: 11.282Focal length of negative lens element 21: −17.309 Focal length ofpositive lens element 22: 7.458 Focal length of positive lens element23: 20.156

TABLE 4 ASPHERICAL SURFACE DATA Surf. No. K A4 A6 1 −1.000 −5.92209E−04−3.49682E−05 2 −1.000 −1.83724E−03 −2.77050E−04 10 0.000  3.35987E−05 2.07529E−05 11 0.000  6.61187E−04  2.50849E−05 Surf. No. A8 A10 1 8.18439E−07 −5.71683E−09 2  2.22940E−05 −5.45134E−07 10 −1.49260E−06 5.03668E−08 11 −2.67851E−06  9.50132E−08

Numerical Embodiment 2

FIGS. 3 through 4D and Tables 5 through 8 show a second numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 3 shows a lens arrangement of the imaging opticalsystem. FIGS. 4A, 4B, 4C and 4D show various aberrations that occurredin the zoom lens system of FIG. 3. Table 5 indicates the surface data,Table 6 indicates various lens system data, Table 7 indicates focallength data, and Table 8 indicates aspherical surface data.

The second numerical embodiment has the same lens arrangement as that ofthe first numerical embodiment except for the following features:

(1) The first lens group G1 has a negative refractive power instead of apositive refractive power.

(2) The positive lens element 12 of the first lens group G1 is apositive meniscus lens element, having a convex surface on the imageside, that is formed from an aspherical glass molded lens element(having an aspherical surface on each side thereof).

(3) The second lens group G2 is configured of a positive lens element21′ formed from a spherical glass lens element, a negative lens element22′ formed from a spherical glass lens element, a positive lens element23′ formed from a spherical glass lens element, and a positive lenselement 24′ formed from an aspherical glass molded lens element (havingan aspherical surface on each side thereof), in that order from theobject side. The positive lens element 21′ is a biconvex positive lenselement. The negative lens element 22′ is a negative meniscus lenselement having a convex surface on the object side, and the positivelens element 23′ is a biconvex positive lens element. The negative lenselement (negative meniscus lens element) 22′ and the positive lenselement (biconvex positive lens element) 23′ are cemented to each other.The positive lens element 24′ is a positive meniscus lens element havinga convex surface on the object side.

TABLE 5 SURFACE DATA Effective Surf. No. r d N(d) νd Aperture  1* 7.9104.123 1.58313 59.5 6.30  2* 2.860 3.109 3.27  3* −11.725 3.500 1.8208042.7 2.81  4* −7.355 −0.425 2.89  5 (Diaphragm) ∞ 2.951 2.79  6 17.1592.352 1.55032 75.5 3.05  7 −19.003 1.610 3.47  8 75.691 1.000 1.9211924.0 4.00  9 6.818 3.602 1.77250 49.6 4.26 10 −16.803 0.307 4.55 116.239 2.480 1.55332 71.7 4.97 12* 8.264 3.160 4.57 13* ∞ 1.900 1.5168064.2 4.17 14 ∞ 0.045 3.93 IM(Imaging Surface) The asterisk (*)designates an aspherical surface which is rotationally symmetrical withrespect to the optical axis.

TABLE 6 VARIOUS LENS SYSTEM DATA f 6.26 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.13Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: −0.03 Focal lengthof entire optical system normalized by the image-sensor size: 1.64

TABLE 7 FOCAL LENGTH DATA Focal length of first lens group G1: −102.869Focal length of second lens group G2: 8.661 Focal length of negativelens element 11: −10.988 Focal length of positive lens element 12:17.663 Focal length of positive lens element 21′: 16.772 Focal length ofnegative lens element 22′: −8.192 Focal length of positive lens element23′: 6.726 Focal length of positive lens element 24′: 32.045

TABLE 8 ASPHERICAL SURFACE DATA Surf. No K A4 A6 1 −1.000 −7.68189E−04−2.77245E−05 2 −1.000 −1.49875E−03 −8.09204E−05 3 −1.000 −1.72566E−03−1.07195E−04 4 −1.000 −8.83476E−04 −7.55926E−06 12 0.000 −4.13067E−04 2.47787E−05 13 0.000 −8.91090E−04  5.73049E−05 Surf. No. A8 A10 1 9.23786E−07 −7.66657E−09  2  1.72640E−07 5.18399E−07 3  2.37421E−06−3.39708E−07  4 −2.28436E−06 1.33515E−07 12 −1.66662E−06 3.17848E−08 13−3.97714E−06 9.35300E−08

Numerical Embodiment 3

FIGS. 5 through 6D and Tables 9 through 12 show a third numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 5 shows a lens arrangement of the imaging opticalsystem. FIGS. 6A, 6B, 6C and 6D show various aberrations that occurredin the zoom lens system of FIG. 5. Table 9 indicates the surface data,Table 10 indicates various lens system data, Table 11 indicates focallength data, and Table 12 indicates aspherical surface data.

The third numerical embodiment has the same lens arrangement as that ofthe second numerical embodiment except for the following feature:

(1) An optical filter OP is provided between the second lens group G2and the cover glass CG.

TABLE 9 SURFACE DATA Effective Surf. No. r d N(d) νd Aperture  1* 7.6464.130 1.58313 59.5 6.27  2* 2.816 3.190 3.25  3* −11.666 2.800 1.8208042.7 2.71  4* −6.72 −0.450 2.77  5 (Diaphragm) ∞ 4.690 2.66  6 28.1262.770 1.55032 75.5 3.82  7 −12.429 0.050 4.28  8 87.122 1.000 1.8466623.8 4.48  9 7.147 3.870 1.77250 49.6 4.71 10 −24.305 0.100 4.92 116.397 2.480 1.55332 71.7 5.16 12* 8.146 1.500 4.72 13* ∞ 1.500 1.5168064.2 4.66 14 ∞ 1.815 4.43 15 ∞ 0.400 1.51680 64.2 4.00 16 ∞ 0.045 3.93IM(Imaging Surface) The asterisk (*) designates an aspherical surfacewhich is rotationally symmetrical with respect to the optical axis.

TABLE 10 VARIOUS LENS SYSTEM DATA f 6.32 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.13Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: −0.02 Focal lengthof entire optical system normalized by the image-sensor size: 1.65

TABLE 11 FOCAL LENGTH DATA Focal length of first lens group G1: −469.168Focal length of second lens group G2: 8.452 Focal length of negativelens element 11: −11.159 Focal length of positive lens element 12:15.385 Focal length of positive lens element 21′: 16.053 Focal length ofnegative lens element 22′: −9.249 Focal length of positive lens element23′: 7.555 Focal length of positive lens element 24′: 35.776

TABLE 12 ASPHERICAL SURFACE DATA Surf. No K A4 A6 1 −1.000 −7.72450E−04−2.88140E−05 2 −1.000 −1.61460E−03 −1.10400E−04 3 −1.000 −2.04860E−03−1.21860E−04 4 −1.000 −1.14890E−03 −1.75890E−05 12 0.000 −3.55960E−04 2.60100E−05 13 0.000 −9.01810E−04  6.93750E−05 Surf. No. A8 A10 1 9.37390E−07 −7.64410E−09  2  5.26170E−06 1.58100E−07 3  1.12110E−06−5.16890E−07  4 −3.12460E−06 1.61930E−07 12 −1.42680E−06 2.25850E−08 13−4.07240E−06 7.98560E−08

Numerical Embodiment 4

FIGS. 7 through 8D and Tables 13 through 16 show a fourth numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 7 shows a lens arrangement of the imaging opticalsystem. FIGS. 8A, 8B, 8C and 8D show various aberrations that occurredin the zoom lens system of FIG. 7. Table 13 indicates the surface data,Table 14 indicates various lens system data, Table 15 indicates focallength data, and Table 16 indicates aspherical surface data.

The fourth numerical embodiment has the same lens arrangement as that ofthe first numerical embodiment except for the following features:

(1) The first lens group G1 has a negative refractive power instead of apositive refractive power.

(2) The positive lens element 12 of the first lens group G1 is apositive meniscus lens element, having a convex surface on the imageside, that is formed from an aspherical glass molded lens element(having an aspherical surface on each side thereof).

(3) The second lens group G2 is configured of a positive lens element21″ formed from a spherical glass lens element, a positive lens element22″ formed from a spherical glass lens element, a negative lens element23″ formed from a spherical glass lens element, a positive lens element24″ formed from a spherical glass lens element, and a positive lenselement 25″ formed from a spherical glass lens element, in that orderfrom the object side. The positive lens element 21″ is a positivemeniscus lens element having a convex surface on the image side. Thepositive lens element 22″ is a biconvex positive lens element. Thenegative lens element 23″ is a biconcave negative lens element and thepositive lens element 24″ is a positive meniscus lens element having aconvex surface on the object side; the negative lens element (biconcavenegative lens element) 23″ and the positive lens element (positivemeniscus lens element) 24″ are cemented to each other. The positive lenselement 25″ is a positive meniscus lens element having a convex surfaceon the object side.

TABLE 13 SURFACE DATA Effective Surf. No. r d N(d) νd Aperture  1* 7.8384.070 1.58313 59.5 6.57  2* 2.767 3.553 3.46  3* −9.748 2.360 1.8208042.7 3.11  4* −7.041 0.452 3.42  5 (Diaphragm) ∞ 3.519 2.82  6 −21.9511.424 1.55032 75.5 3.08  7 −8.208 2.096 3.18  8 10.873 3.676 1.5503275.5 4.28  9 −32.839 0.050 4.43 10 −56.671 1.000 1.84666 23.8 4.43 118.367 3.259 1.77250 49.6 4.55 12 124.293 0.100 4.71 13 7.775 2.4301.77250 49.6 5.03 14 15.057 3.000 4.68 15 ∞ 1.900 1.51680 64.2 4.20 16 ∞0.045 3.93 IM(Imaging Surface) The asterisk (*) designates an asphericalsurface which is rotationally symmetrical with respect to the opticalaxis.

TABLE 14 VARIOUS LENS SYSTEM DATA f 6.26 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm):0.13Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: −0.01 Focal lengthof entire optical system normalized by the image-sensor size: 1.64

TABLE 15 FOCAL LENGTH DATA Focal length of first lens group G1: −33.746Focal length of second lens group G2: 8.609 Focal length of negativelens element 11: −10.417 Focal length of positive lens element 12:22.171 Focal length of positive lens element 21″ 7.838 Focal length ofpositive lens element 22″ 15.300 Focal length of negative lens element23″ −8.551 Focal length of positive lens element 24″ 11.473 Focal lengthof positive lens element 25″ 18.168

TABLE 16 ASPHERICAL SURFACE DATA Surf. No. K A4 A6 1 −1.000 −6.89798E−04−2.32004E−05 2 −1.000 −4.96111E−04 −1.16038E−04 3 −1.000 −1.45785E−03−8.37288E−05 4 −1.000 −9.21826E−04 −2.13943E−05 Surf. No. A8 A10 16.59414E−07 −4.66118E−09 2 6.54900E−06 −4.91580E−08 3 4.66001E−08−3.99011E−07 4 −1.49741E−06   2.91835E−08

Numerical Embodiment 5

FIGS. 9 through 10D and Tables 17 through 20 show a fifth numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 9 shows a lens arrangement of the imaging opticalsystem. FIGS. 10A, 10B, 10C and 10D show various aberrations thatoccurred in the zoom lens system of FIG. 9. Table 17 indicates thesurface data, Table 18 indicates various lens system data, Table 19indicates focal length data, and Table 20 indicates aspherical surfacedata.

The fifth numerical embodiment has the same lens arrangement as that ofthe first numerical embodiment except for the following features:

(1) The first lens group G1 is configured of a negative lens element 11′formed from an aspherical glass molded lens element (having anaspherical surface on each side thereof), a positive lens element 12′formed from a spherical glass lens element, a negative lens element 13′formed from a spherical glass lens element, and a positive lens element14′ formed from a spherical glass lens element, in that order from theobject side. The aspherical surface on the object side of the negativelens element 11′ includes a paraxial convex surface convexing toward theobject side, a paraxial curvature (curvature of the central portion)that is the greatest within the effective aperture, and a portion withinthe effective aperture (at a peripheral portion other than the paraxialportion) that has a curvature that is less than ½ of the paraxialcurvature (curvature of the central portion). The positive lens element12′ is a positive meniscus lens element having a convex surface on theimage side. The negative lens element 13′ is a negative meniscus lenselement having a convex surface on the image side. The positive lenselement 14′ is a biconvex positive lens element.

(2) The second lens group G2 is configured of a positive lens element21A formed from a spherical glass lens element, a negative lens element22A formed from a spherical glass lens element, a positive lens element23A formed from spherical glass lens element and a positive lens element24A formed from spherical glass lens element, in that order from theobject side. The positive lens element 21A is a biconvex positive lenselement. The negative lens element 22A is a biconcave negative lenselement, and the positive lens element 23A is a biconvex positive lenselement; the negative lens element (biconcave negative lens element) 22Aand the positive lens element (biconvex positive lens element) 23A arecemented to each other. The positive lens element 24A is a positivemeniscus lens element having a convex surface on the object side.

TABLE 17 SURFACE DATA Effective Surf. No. r d N(d) νd Aperture  1* 8.2604.070 1.58313 59.5 6.46  2* 3.081 3.579 3.45  3 −10.417 2.360 1.9108235.3 2.88  4 −9.252 0.571 3.17  5 −5.782 2.066 1.55032 75.5 3.16  6−8.688 0.050 3.60  7 53.769 3.000 1.55032 75.5 3.67  8 −9.907 0.850 3.71 9 (Diaphragm) ∞ 4.441 3.38 10 10.713 4.792 1.55032 75.5 5.36 11 −16.9790.165 5.32 12 −15.718 1.000 1.84666 23.8 5.29 13 13.53 3.449 1.7725049.6 5.45 14 −51.443 0.100 5.59 15 8.178 2.430 1.77250 49.6 5.70 1618.668 3.046 5.38 17 ∞ 1.900 1.51680 64.2 4.44 18 ∞ 0.045 3.94IM(Imaging Surface) The asterisk (*) designates an aspherical surfacewhich is rotationally symmetrical with respect to the optical axis.

TABLE 18 VARIOUS LENS SYSTEM DATA f 6.26 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element11′ (paraxial curvature/curvature of paraxial convex surface) [1/mm]:0.12 Curvature at, or in the vicinity of, effective aperture of surfaceon the object side of the negative lens element 11′ (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: −0.07 Focal lengthof entire optical system normalized by the image-sensor size: 1.64

TABLE 19 FOCAL LENGTH DATA Focal length of first lens group G1: 28.746Focal length of second lens group G2: 11.505 Focal length of negativelens element 11′: −11.857 Focal length of positive lens element 12′:46.207 Focal length of negative lens element 13′: −42.015 Focal lengthof positive lens element 14′: 15.460 Focal length of positive lenselement 21A: 12.717 Focal length of negative lens element 22A: −8.455Focal length of positive lens element 23A: 14.196 Focal length ofpositive lens element 24A: 17.112

TABLE 20 ASPHERICAL SURFACE DATA Surf. No K A4 A6 1 −1.000 −5.72301E−04−1.78820E−05 2 −1.000 −3.69277E−04 −5.68434E−05 Surf. No. A8 A10 14.64073E−07 −3.16690E−09 2 2.03815E−06  1.39353E−07

Numerical Embodiment 6

FIGS. 11 through 12D and Tables 21 through 24 show a sixth numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 11 shows a lens arrangement of the imaging opticalsystem. FIGS. 12A, 12B, 12C and 12D show various aberrations thatoccurred in the zoom lens system of FIG. 11. Table 21 indicates thesurface data, Table 22 indicates various lens system data, Table 23indicates focal length data, and Table 24 indicates aspherical surfacedata.

The sixth numerical embodiment has the same lens arrangement as that ofthe first numerical embodiment except for the following features:

(1) The first lens group G1 has a negative refractive power instead of apositive refractive power.

(2) The positive lens element 12 of the first lens group G1 is apositive meniscus lens element, having a convex surface on the imageside, that is formed from an aspherical glass molded lens element(having an aspherical surface on each side thereof).

(3) The second lens group G2 is configured of a positive lens element21B formed from a spherical glass lens element, a negative lens element22B formed from a spherical glass lens element, a positive lens element23B formed from a spherical glass lens element, and a positive lenselement 24B formed from spherical glass lens element, in that order fromthe object side. The positive lens element 21B is a biconvex positivelens element. The negative lens element 22B is a negative meniscus lenselement having a convex surface on the object side, and the positivelens element 23B is a positive meniscus lens element having a convexsurface on the object side; the negative lens element (negative meniscuslens element) 22B and the positive lens element (positive meniscus lenselement) 23B are cemented to each other. The positive lens element 24Bis a positive meniscus lens element having a convex surface on theobject side.

(4) An optical filter OP is provided between the second lens group G2and the cover glass CG.

TABLE 21 SURFACE DATA Effective Surf. No. r d N(d) νd Aperture  1* 5.6613.869 1.58313 59.5 6.59  2* 2.445 3.918 3.61  3* −8.553 2.500 1.8820237.2 3.30  4 * −7.324 0.340 3.52  5 (Diaphragm) ∞ 3.569 2.95  6 25.084.100 1.55032 75.5 2.99  7 −10.986 0.138 3.93  8 15.231 1.000 1.9228620.9 4.29  9 6.525 3.734 1.77250 49.6 4.25 10 28.103 0.100 4.38 11 8.6543.665 1.55032 75.5 4.63 12 123.416 1.000 4.41 13 ∞ 0.400 1.51680 64.24.29 14 ∞ 2.434 4.26 15 ∞ 0.400 1.51680 64.2 3.96 16 ∞ 0.045 3.93IM(Imaging Surface) The asterisk (*) designates an aspherical surfacewhich is rotationally symmetrical with respect to the optical axis.

TABLE 22 VARIOUS LENS SYSTEM DATA f 6.26 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.18Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: −0.03 Focal lengthof entire optical system normalized by the image-sensor size: 1.64

TABLE 23 FOCAL LENGTH DATA Focal length of first lens group G1: −35.594Focal length of second lens group G2: 7.882 Focal length of negativelens element 11: −13.252 Focal length of positive lens element 12:29.576 Focal length of positive lens element 21B: 14.466 Focal length ofnegative lens element 22B: −13.090 Focal length of positive lens element23B: 10.228 Focal length of positive lens element 24B: 16.722

TABLE 24 ASPHERICAL SURFACE DATA Surf. No. K A3 A4 A6 1 −1.0000.00000E+00 −3.47741E−04 −1.38749E−05 2 −1.000 0.00000E+00 2.34139E−04−1.57714E−04 3 −1.000 9.86161E−05 −8.50683E−04 −1.57785E−04 4 −1.0002.60017E−04 −6.84008E−04 −8.48713E−06 Surf. No. A8 A10 A12 A14 1−1.44077E−06 7.07668E−08 −1.15489E−09 6.76641E−12 2 −1.79401E−052.77809E−06 −1.31636E−07 2.61888E−09 3 2.17920E−05 −2.65296E−061.86141E−07 −5.85140E−09 4 −2.46909E−08 −8.37064E−08 1.25123E−08−5.52069E−10

Numerical Embodiment 7

FIGS. 13 through 14D and Tables 25 through 28 show a seventh numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 13 shows a lens arrangement of the imaging opticalsystem. FIGS. 14A, 14B, 14C and 14D show various aberrations thatoccurred in the zoom lens system of FIG. 13. Table 25 indicates thesurface data, Table 26 indicates various lens system data, Table 27indicates focal length data, and Table 28 indicates aspherical surfacedata.

The seventh numerical embodiment has the same lens arrangement as thatof the first numerical embodiment except for the following features:

(1) The first lens group G1 has a negative refractive power instead of apositive refractive power.

(2) The positive lens element 12 of the first lens group G1 is apositive meniscus lens element, having a convex surface on the imageside, that is formed from an aspherical glass molded lens element(having an aspherical surface on each side thereof).

(3) The second lens group G2 is configured of a positive lens element21C formed from a spherical glass lens element, a positive lens element22C formed from a spherical glass lens element, a negative lens element23C formed from a spherical glass lens element, and a positive lenselement 24C formed from a spherical glass lens element, in that orderfrom the object side. The positive lens element 21C is a biconvexpositive lens element. The positive lens element 22C is a biconvexpositive lens element and the negative lens element 23C is a biconcavenegative lens element; the positive lens element (biconvex positive lenselement) 22C and the negative lens element (biconcave negative lenselement) 23C are cemented to each other. The positive lens element 24Cis a positive meniscus lens element having a convex surface on theobject side.

TABLE 25 SURFACE DATA Effective Surf. No. r d N(d) νd Aperture  1* 8.0503.000 1.80139 45.5 5.10  2* 3.120 2.351 3.15  3* −12.575 3.000 1.8208042.7 3.00  4* −7.65 −0.360 3.17  5 (Diaphragm) ∞ 7.206 3.00  6 21.0364.000 1.55032 75.5 4.41  7 −13.181 0.100 5.00  8 13.407 3.881 1.5891361.3 5.30  9 −13.407 1.400 1.92286 20.9 5.17 10 113.853 0.100 5.20 118.194 3.413 1.55032 75.5 5.33 12 16.595 4.464 4.80 13 ∞ 0.400 1.5168064.2 3.99 14 ∞ 0.045 3.94 IM (Imaging Surface) The asterisk (*)designates an aspherical surface which is rotationally symmetrical withrespect to the optical axis.

TABLE 26 VARIOUS LENS SYSTEM DATA f 6.26 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.12Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: 0.02 Focal lengthof entire optical system normalized by the image-sensor size: 1.64

TABLE 27 FOCAL LENGTH DATA Focal length of first lens group G1: −28.321Focal length of second lens group G2: 8.807 Focal length of negativelens element 11: −8.718 Focal length of positive lens element 12: 18.671Focal length of positive lens element 21C: 15.363 Focal length ofpositive lens element 22C: 12.024 Focal length of negative lens element23C: −12.929 Focal length of positive lens element 24C: 25.708

TABLE 28 ASPHERICAL SURFACE DATA Surf. No. K A3 A4 A6 1 −1.0000.00000E+00 −1.17811E−03 −1.17392E−04 2 −1.000 0.00000E+00 −7.43680E−04−3.38404E−05 3 −1.000 0.00000E+00 −1.51525E−03 −2.24627E−05 4 −1.0000.00000E+00 −2.99872E−03 −1.10455E−04 Surf. No. A8 A10 A12 A14 19.67332E−07 1.33292E−07 1.29888E−08 0.00000E+00 2 −7.41479E−081.54911E−07 −8.66691E−09 0.00000E+00 3 3.97479E−07 7.16787E−08−2.36168E−09 2.02749E−11 4 6.99873E−06 2.03734E−06 −3.11172E−071.84754E−08

Numerical Embodiment 8

FIGS. 15 through 16D and Tables 29 through 32 show an eighth numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 15 shows a lens arrangement of the imaging opticalsystem. FIGS. 16A, 16B, 16C and 16D show various aberrations thatoccurred in the zoom lens system of FIG. 15. Table 29 indicates thesurface data, Table 30 indicates various lens system data, Table 31indicates focal length data, and Table 32 indicates aspherical surfacedata.

The eighth numerical embodiment has the same lens arrangement as that ofthe first numerical embodiment except for the following features:

(1) The first lens group G1 has a negative refractive power instead of apositive refractive power.

(2) The positive lens element 12 of the first lens group G1 is apositive meniscus lens element, having a convex surface on the imageside, that is formed from an aspherical glass molded lens element(having an aspherical surface on each side thereof).

(3) The second lens group G2 is configured of a positive lens element21D formed from a spherical glass lens element, a positive lens element22D formed from a spherical glass lens element, a negative lens element23D formed from a spherical glass lens element, and a positive lenselement 24D formed from an aspherical glass molded lens element (havingan aspherical surface on each side thereof), in that order from theobject side. The positive lens element 21D is a biconvex positive lenselement. The positive lens element 22D is a biconvex positive lenselement, and the negative lens element 23D is a biconcave negative lenselement; the positive lens element (biconvex positive lens element) 22Dand the negative lens element (biconcave negative lens element) 23D arecemented to each other. The positive lens element 24D is a biconvexpositive lens element.

TABLE 29 SURFACE DATA Effective Surf. No. r d N(d) νd Aperture  1* 6.2593.700 1.80139 45.5 5.87  2* 2.710 2.930 3.10  3* −7.403 2.822 1.8513540.1 2.82  4* −6.754 −0.254 3.07  5 (Diaphragm) ∞ 3.474 2.85  6 20.3463.422 1.55032 75.5 3.03  7 −10.46 0.100 3.75  8 10.851 3.357 1.6584450.9 4.13  9 −10.851 1.000 1.84666 23.8 4.07 10 14.583 1.285 4.10 117.063 2.861 1.55332 71.7 4.83 12* −83.869 3.658 4.71 13* ∞ 0.400 1.5168064.2 3.98 14 ∞ 0.045 3.93 IM (Imaging Surface) The asterisk (*)designates an aspherical surface which is rotationally symmetrical withrespect to the optical axis.

TABLE 30 VARIOUS LENS SYSTEM DATA f 6.26 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.16Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: −1.09 Focal lengthof entire optical system normalized by the image-sensor size: 1.64

TABLE 31 FOCAL LENGTH DATA Focal length of first lens group G1: −25.345Focal length of second lens group G2: 7.895 Focal length of negativelens element 11: −11.123 Focal length of positive lens element 12:30.158 Focal length of positive lens element 21D: 13.068 Focal length ofpositive lens element 22D: 8.779 Focal length of negative lens element23D: −7.218 Focal length of positive lens element 24D: 11.907

TABLE 32 ASPHERICAL SURFACE DATA Surf. No. K A3 A4 A6 1 −1.0000.00000E+00 −3.79799E−04 −1.13353E−05 2 −1.000 0.00000E+00 8.03159E−05−2.27561E−04 3 −1.000 0.00000E+00 −1.65137E−03 −1.82980E−04 4 −1.0000.00000E+00 −8.54271E−04 −4.96999E−05 12 0.000 0.00000E+00 −2.44234E−041.78643E−06 13 0.000 0.00000E+00 −1.55469E−04 2.18036E−05 Surf. No. A8A10 A12 A14 1 −8.89522E−07 4.73436E−08 −7.30848E−10 3.84216E−12 23.04046E−05 −3.87017E−06 3.30234E−07 −8.34750E−09 3 2.24647E−05−2.69113E−06 8.72112E−08 0.00000E+00 4 6.34259E−06 −6.66119E−072.46417E−08 0.00000E+00 12 −9.03745E−08 −8.31728E−10 0.00000E+000.00000E+00 13 −6.95018E−07 7.84930E−09 0.00000E+00 0.00000E+00

Numerical Embodiment 9

FIGS. 17 through 18D and Tables 33 through 36 show a ninth numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 17 shows a lens arrangement of the imaging opticalsystem. FIGS. 18A, 18B, 18C and 18D show various aberrations thatoccurred in the zoom lens system of FIG. 17. Table 33 indicates thesurface data, Table 34 indicates various lens system data, Table 35indicates focal length data, and Table 36 indicates aspherical surfacedata.

The ninth numerical embodiment has the same lens arrangement as that ofthe eighth numerical embodiment except for the following feature:

(1) The positive lens element 24D of the second lens group G2 is apositive meniscus lens element having a convex surface on the objectside.

TABLE 33 SURFACE DATA Effective Surf. No. r d N(d) νd Aperture  1* 5.7253.700 1.58313 59.5 6.07  2* 2.401 3.170 3.21  3* −8.306 2.960 1.8208042.7 2.94  4* −7.524 −0.510 3.06  5 (Diaphragm) ∞ 4.510 2.99  6 24.343.050 1.55032 75.5 3.40  7 −10.063 0.100 3.97  8 11.469 3.450 1.5891361.3 4.35  9 −11.469 1.000 1.84666 23.8 4.31 10 27.671 1.420 4.38 117.931 2.770 1.55332 71.7 4.95 12* 765 3.935 4.77 13* ∞ 0.400 1.5168064.2 3.98 14 ∞ 0.045 3.93 IM (Imaging Surface) The asterisk (*)designates an aspherical surface which is rotationally symmetrical withrespect to the optical axis.

TABLE 34 VARIOUS LENS SYSTEM DATA f 6.28 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.17Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: −0.05 Focal lengthof entire optical system normalized by the image-sensor size: 1.64

TABLE 35 FOCAL LENGTH DATA Focal length of first lens group G1: −25.042Focal length of second lens group G2: 8.092 Focal length of negativelens element 11: −12.020 Focal length of positive lens element 12:35.977 Focal length of positive lens element 21D: 13.357 Focal length ofpositive lens element 22D: 10.309 Focal length of negative lens element23D: −9.466 Focal length of positive lens element 24D: 14.465

TABLE 36 ASPHERICAL SURFACE DATA Surf. No. K A3 A4 A6 1 −1.0000.00000E+00 −5.87800E−04 −2.19240E−05 2 −1.000 0.00000E+00 −1.84270E−05−4.00680E−04 3 −1.000 0.00000E+00 −1.30600E−03 −9.40530E−05 4 −1.0000.00000E+00 −6.83630E−04 −6.90430E−06 12 0.000 0.00000E+00 −6.40600E−056.29090E−06 13 0.000 0.00000E+00 −4.54950E−05 2.68090E−05 Surf. No. A8A10 A12 A14 1 −1.01330E−06 7.93010E−08 −1.66940E−09 1.22390E−11 26.37420E−05 −9.10110E−06 8.30070E−07 −2.94460E−08 3 7.16250E−06−4.58590E−07 −6.16250E−09 0.00000E+00 4 −1.68400E−06 2.60850E−07−1.31260E−08 0.00000E+00 12 −8.97570E−08 −1.06430E−09 0.00000E+000.00000E+00 13 −8.46770E−07 6.24780E−09 0.00000E+00 0.00000E+00

Numerical Embodiment 10

FIGS. 19 through 20D and Tables 37 through 40 show a tenth numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 19 shows a lens arrangement of the imaging opticalsystem. FIGS. 20A, 20B, 20C and 20D show various aberrations thatoccurred in the zoom lens system of FIG. 19. Table 37 indicates thesurface data, Table 38 indicates various lens system data, Table 39indicates focal length data, and Table 40 indicates aspherical surfacedata.

The tenth numerical embodiment has the same lens arrangement as that ofthe eighth numerical embodiment.

TABLE 37 SURFACE DATA Effective Surf. No. r d N(d) νd Aperture  1* 5.5632.893 1.58913 61.3 5.53  2* 2.756 3.376 3.22  3* −6.672 2.247 1.8513540.1 2.52  4* −6.399 −0.434 2.53  5 (Diaphragm) ∞ 3.102 2.48  6 62.1613.123 1.59282 68.6 3.46  7 −8.555 0.100 4.06  8 12.136 3.189 1.8348142.7 4.40  9 −15.408 0.800 1.94595 18.0 4.30 10 20.604 0.409 4.24 1114.263 4.115 1.55332 71.7 4.32 12* −135.674 3.055 4.26 13* ∞ 0.4001.51680 64.2 3.95 14 ∞ 0.045 3.93 IM (Imaging Surface) The asterisk (*)designates an aspherical surface which is rotationally symmetrical withrespect to the optical axis.

TABLE 38 VARIOUS LENS SYSTEM DATA f 6.27 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.18Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: 0.03 Focal lengthof entire optical system normalized by the image-sensor size: 1.64

TABLE 39 FOCAL LENGTH DATA Focal length of first lens group G1: −34.478Focal length of second lens group G2: 7.466 Focal length of negativelens element 11: −15.002 Focal length of positive lens element 12:38.389 Focal length of positive lens element 21D: 12.897 Focal length ofpositive lens element 22D: 8.584 Focal length of negative lens element23D: −9.220 Focal length of positive lens element 24D: 23.555

TABLE 40 ASPHERICAL SURFACE DATA Surf. No. K A3 A4 A6 1 −1.000−2.89349E−04 −8.99891E−04 −5.60232E−05 2 −1.000 0.00000E+00 −2.00874E−03−8.11287E−05 3 −1.000 0.00000E+00 −2.28195E−03 7.94055E−05 4 −1.0000.00000E+00 −9.54252E−04 2.96517E−05 12 0.000 0.00000E+00 −2.53188E−042.31737E−05 13 0.000 0.00000E+00 −1.62301E−03 1.05056E−04 Surf. No. A8A10 A12 A14 1 4.18669E−07 1.19427E−07 −4.20148E−09 4.38636E−11 2−3.54775E−05 9.91674E−06 −8.21335E−07 2.57290E−08 3 −3.97875E−057.22797E−06 −4.44000E−07 0.00000E+00 4 −6.27985E−06 7.83979E−07−3.51431E−08 0.00000E+00 12 −1.48152E−06 4.24313E−08 −3.95478E−100.00000E+00 13 −2.80912E−06 −1.56731E−08 1.82684E−09 0.00000E+00

Numerical Embodiment 11

FIGS. 21 through 22D and Tables 41 through 44 show a eleventh numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 21 shows a lens arrangement of the imaging opticalsystem. FIGS. 22A, 22B, 22C and 22D show various aberrations thatoccurred in the zoom lens system of FIG. 21. Table 41 indicates thesurface data, Table 42 indicates various lens system data, Table 43indicates focal length data, and Table 44 indicates aspherical surfacedata.

The eleventh numerical embodiment has the same lens arrangement as thatof the eighth numerical embodiment except for the following feature:

(1) The biconvex positive lens element 21D of the second lens group G2is formed from an aspherical glass molded lens element (having anaspherical surface on each side thereof).

TABLE 41 SURFACE DATA Effective Surf. No. r d N (d) νd Aperture  1*5.518 3.251 1.55332 71.7 5.70  2* 2.493 3.376 3.11  3* −6.802 1.8641.77377 47.2 2.54  4* −6.11 −0.418 2.56  5 (Diaphragm) ∞ 2.806 2.48  6106.266 3.965 1.55332 71.7 3.19  7* −6.707 0.100 4.04  8* 11.768 3.1801.72916 54.7 4.40  9 −16.455 1.000 1.92286 20.9 4.32 10 20.581 0.3824.29 11 14.381 3.494 1.55332 71.7 4.40 12* −88.174 3.555 4.39 13* ∞0.400 1.51680 64.2 3.96 14 ∞ 0.045 3.93 IM (Imaging Surface) Theasterisk (*) designates an aspherical surface which is rotationallysymmetrical with respect to the optical axis.

TABLE 42 VARIOUS LENS SYSTEM DATA f 6.38 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.18Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: −0.26 Focal lengthof entire optical system normalized by the image-sensor size: 1.67

TABLE 43 FOCAL LENGTH DATA Focal length of first lens group G1: −27.904Focal length of second lens group G2: 7.404 Focal length of negativelens element 11: −13.321 Focal length of positive lens element 12:35.686 Focal length of positive lens element 21D: 11.547 Focal length ofpositive lens element 22D: 9.879 Focal length of negative lens element23D: −9.782 Focal length of positive lens element 24D: 22.620

TABLE 44 ASPHERICAL SURFACE DATA Surf. No. K A3 A4 A6 1 −1.000−4.80105E−04 −6.52202E−04 −6.82464E−05 2 −1.000 0.00000E+00 −1.10134E−03−8.64999E−05 3 −1.000 0.00000E+00 −1.80327E−03 −1.73512E−04 4 −1.0000.00000E+00 −9.40848E−04 −2.99926E−05 7 0.000 0.00000E+00 −8.63069E−054.02963E−06 8 0.000 0.00000E+00 1.64014E−04 9.45447E−06 12 0.0000.00000E+00 −3.14502E−04 3.55676E−05 13 0.000 0.00000E+00 −2.04304E−031.27658E−04 Surf. No. A8 A10 A12 A14 1 1.23824E−06 6.69905E−08−2.72200E−09 2.88840E−11 2 −4.73374E−05 1.27235E−05 −9.80526E−072.37229E−08 3 3.19188E−05 −4.65007E−06 1.76472E−07 0.00000E+00 4−8.61362E−07 1.07511E−07 −1.75149E−08 0.00000E+00 7 −1.69777E−062.36113E−08 0.00000E+00 0.00000E+00 8 −4.11245E−07 −7.57629E−090.00000E+00 0.00000E+00 12 −1.59155E−06 2.40321E−08 0.00000E+000.00000E+00 13 −4.14327E−06 5.64850E−08 0.00000E+00 0.00000E+00

Numerical Embodiment 12

FIGS. 23 through 24D and Tables 45 through 48 show a twelfth numericalembodiment of the imaging optical system, according to the presentinvention. FIG. 23 shows a lens arrangement of the imaging opticalsystem. FIGS. 24A, 24B, 24C and 24D show various aberrations thatoccurred in the zoom lens system of FIG. 23. Table 45 indicates thesurface data, Table 46 indicates various lens system data, Table 47indicates focal length data, and Table 48 indicates aspherical surfacedata.

The twelfth numerical embodiment has the same lens arrangement as thatof the ninth numerical embodiment.

TABLE 45 SURFACE DATA Effective Surf. No. r d N (d) νd Aperture  1*5.500 3.537 1.58313 59.5 5.74  2* 2.572 2.917 3.12  3* −7.351 2.8211.55332 71.7 2.77  4* −6.5 −0.419 2.52  5 (Diaphragm) ∞ 3.199 2.48  620.209 3.397 1.59282 68.6 3.93  7 −9.695 0.100 4.31  8 10.378 3.8151.59282 68.6 4.40  9 −10.378 1.000 1.92286 20.9 4.28 10 587.159 0.3494.33 11 16.685 2.200 1.55332 71.7 4.38 12* 224.469 3.639 4.25 13* ∞0.400 1.51680 64.2 3.95 14 ∞ 0.045 3.93 IM (Imaging Surface) Theasterisk (*) designates an aspherical surface which is rotationallysymmetrical with respect to the optical axis.

TABLE 46 VARIOUS LENS SYSTEM DATA f 6.61 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.18Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: −0.07 Focal lengthof entire optical system normalized by the image-sensor size: 1.73

TABLE 47 FOCAL LENGTH DATA Focal length of first lens group G1: −27.745Focal length of second lens group G2: 7.381 Focal length of negativelens element 11: −14.924 Focal length of positive lens element 12:46.524 Focal length of positive lens element 21D: 11.540 Focal length ofpositive lens element 22D: 9.395 Focal length of negative lens element23D: −9.220 Focal length of positive lens element 24D: 32.453

TABLE 48 ASPHERICAL SURFACE DATA Surf. No. K A3 A4 A6 1 −1.000−1.93345E−04 −6.60222E−04 −3.25902E−05 2 −1.000 0.00000E+00 −2.24645E−039.65534E−05 3 −1.000 0.00000E+00 −2.20620E−03 −6.27326E−06 4 −1.0000.00000E+00 −9.71837E−04 1.18419E−04 12 0.000 0.00000E+00 −5.74002E−046.78388E−05 13 0.000 0.00000E+00 −1.60217E−03 1.30989E−04 Surf. No. A8A10 A12 A14 1 −1.38790E−06 1.30847E−07 −3.00640E−09 2.31405E−11 2−8.11262E−05 1.33573E−05 −8.61099E−07 2.38868E−08 3 4.17157E−075.80187E−07 −4.65725E−08 0.00000E+00 4 −3.10838E−05 4.44148E−06−2.37080E−07 0.00000E+00 12 −2.25051E−06 −1.01473E−08 1.55364E−090.00000E+00 13 −1.66970E−06 −1.74956E−07 6.00202E−09 0.00000E+00

Numerical Embodiment 13

FIGS. 25 through 26D and Tables 49 through 52 show a thirteenthnumerical embodiment of the imaging optical system, according to thepresent invention. FIG. 25 shows a lens arrangement of the imagingoptical system. FIGS. 26A, 26B, 26C and 26D show various aberrationsthat occurred in the zoom lens system of FIG. 25. Table 49 indicates thesurface data, Table 50 indicates various lens system data, Table 51indicates focal length data, and Table 52 indicates aspherical surfacedata.

The thirteenth numerical embodiment has the same lens arrangement asthat of the ninth numerical embodiment except for the following feature:

(1) The negative lens element 23D of the second lens group G2 is anegative meniscus lens element having a convex surface on the imageside.

TABLE 49 SURFACE DATA Effective Surf. No. r d N (d) νd Aperture  1*4.700 3.200 1.58313 59.5 5.26  2* 2.239 2.709 2.76  3* −6.726 1.8501.82080 42.7 2.37  4* −6.702 −0.304 2.32  5 (Diaphragm) ∞ 2.427 2.26  620.061 3.286 1.55032 75.5 3.39  7 −8.185 0.100 3.93  8 9.794 3.8521.65844 50.9 4.20  9 −9.794 0.700 1.94595 18.0 4.11 10 −855.909 0.3594.16 11 13.728 1.743 1.55332 71.7 4.21 12* 61.506 3.633 4.17 13* ∞ 0.4001.51680 64.2 3.94 14 ∞ 0.045 3.92 IM (Imaging Surface) The asterisk (*)designates an aspherical surface which is rotationally symmetrical withrespect to the optical axis.

TABLE 50 VARIOUS LENS SYSTEM DATA f 6.38 FNO. 1.60 W 50 Y 3.82 Curvatureat central portion on surface on object side of negative lens element 11(paraxial curvature/curvature of paraxial convex surface) [1/mm]: 0.21Curvature at, or in the vicinity of, effective aperture of surface onthe object side of the negative lens element 11 (i.e., an examplecurvature at an outermost peripheral portion) [1/mm]: 0.00 Focal lengthof entire optical system normalized by the image-sensor size: 1.67

TABLE 51 FOCAL LENGTH DATA Focal length of first lens group G1: −21.042Focal length of second lens group G2: 6.507 Focal length of negativelens element 11: −14.065 Focal length of positive lens element 12:63.958 Focal length of positive lens element 21D: 11.018 Focal length ofpositive lens element 22D: 8.067 Focal length of negative lens element23D: −10.478 Focal length of positive lens element 24D: 31.530

TABLE 52 ASPHERICAL SURFACE DATA Surf. No. K A3 A4 A6 1 −1.000−2.75814E−04 −4.78259E−04 −1.73307E−05 2 −1.000 0.00000E+00 −1.45649E−031.00529E−03 3 −1.000 0.00000E+00 −3.04409E−03 2.82701E−04 4 −1.0000.00000E+00 −1.69283E−03 2.58587E−04 12 0.000 0.00000E+00 −1.15075E−031.08111E−04 13 0.000 0.00000E+00 −2.19775E−03 2.12333E−04 Surf. No. A8A10 A12 A14 1 −5.70212E−06 4.02511E−07 −1.01861E−08 9.41926E−11 2−5.02109E−04 9.37772E−05 −7.33965E−06 2.03370E−07 3 −1.20934E−042.02118E−05 −1.31318E−06 0.00000E+00 4 −9.22176E−05 1.50890E−05−9.29631E−07 0.00000E+00 12 −5.85477E−06 1.12073E−07 0.00000E+000.00000E+00 13 −9.74758E−06 1.73312E−07 0.00000E+00 0.00000E+00

The numerical values of each condition for each embodiment are shown inTable 53.

TABLE 53 Embod. 1 Embod. 2 Embod. 3 Embod. 4 Condition (1) 1.11 1.261.21 1.25 Condition (2) 0.79 0.66 0.65 0.65 Condition (3) −1.43 −1.76−1.77 −1.66 Condition (4) 75.5 75.5 75.5 75.5 Condition (5) −0.06 0.110.02 0.31 Condition (6) 0.52 0.47 0.46 0.48 Embod. 5 Embod. 6 Embod. 7Embod. 8 Embod. 9 Condition (1) 1.32 0.90 1.29 1.00 0.91 Condition (2)0.65 0.62 0.48 0.59 0.59 Condition (3) −1.89 −2.12 −1.39 −1.78 −1.91Condition (4) 75.5 75.5 75.5 75.5 75.5 Condition (5) −0.41 0.37 0.310.44 0.48 Condition (6) 0.46 0.40 0.44 0.40 0.41 Embod. 10 Embod. 11Embod. 12 Embod. 13 Condition (1) 0.89 0.87 0.83 0.74 Condition (2) 0.460.51 0.53 0.50 Condition (3) −2.39 −2.09 −2.26 −2.20 Condition (4) 68.671.7 68.6 75.5 Condition (5) 0.44 0.48 0.54 0.67 Condition (6) 0.34 0.380.36 0.35

As can be understood from Table 53, the first through thirteenthnumerical embodiments satisfy conditions (1) through (6). Furthermore,as can be understood from the aberration diagrams, the variousaberrations are suitably corrected.

Obvious changes may be made in the specific embodiments of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

What is claimed is:
 1. An imaging optical system comprising a positiveor negative first lens group, an aperture diaphragm, and a positivesecond lens group, in that order from the object side, wherein saidfirst lens group includes a negative lens element provided closest tothe object side within said first lens group, wherein the negative lenselement that is closest to the object side includes an asphericalsurface on the object side thereof, said aspherical surface including aparaxial convex surface convexing toward the object side, a paraxialcurvature that is the greatest within the effective aperture, and aportion within the effective aperture that has a curvature that is lessthan ½ of the paraxial curvature, and wherein the following conditions(1), (2), (3) and (6) are satisfied:R1/f<1.35  (1),D1/f>0.4  (2),−2.5<f1/f<−1.3  (3), and0.3<(R1−R2)/(R1+R2)<0.55  (6), wherein f designates the focal length ofsaid imaging optical system, f1 designates the focal length of thenegative lens element provided closest to the object side within saidfirst lens group, D1 designates a thickness, along the optical axis, ofsaid negative lens element provided closest to the object side withinsaid first lens group, R1 designates the paraxial radius of curvature ofthe surface on the object side of said negative lens element providedclosest to the object side within said first lens group, and R2designates the paraxial radius of curvature of the surface on the imageside of said negative lens element provided closest to the object sidewithin said first lens group.
 2. The imaging optical system according toclaim 1, wherein the following condition (5) is satisfied:−0.45<f1/fg1<1  (5), wherein f1 designates the focal length of saidnegative lens element provided closest to the object side within saidfirst lens group, and fg1 designates the focal length of said first lensgroup.
 3. The imaging optical system according to claim 1, wherein saidfirst lens group includes a positive lens element behind said negativelens element provided closest to the object side within said first lensgroup.
 4. The imaging optical system according to claim 3, wherein saidpositive lens element that is provided behind said negative lens elementprovided closest to the object side, within said first lens group, is apositive meniscus lens element having a convex surface on the imageside.
 5. The imaging optical system according to claim 3, wherein saidpositive lens element that is provided behind said negative lens elementprovided closest to the object side, within said first lens group, hasan Abbe number of at least 35 with respect to the d-line.
 6. The imagingoptical system according to claim 1, wherein said second lens groupincludes at least one positive lens element that has an Abbe number ofat least 70 with respect to the d-line.
 7. The imaging optical systemaccording to claim 1, wherein said second lens group includes at leastone negative lens element that has an Abbe number of 20 or less withrespect to the d-line.
 8. An imaging optical system comprising apositive or negative first lens group, an aperture diaphragm, and apositive second lens group, in that order from the object side, whereinsaid first lens group includes a negative lens element provided closestto the object side within said first lens group, wherein the negativelens element that is closest to the object side includes an asphericalsurface on the object side thereof, said aspherical surface including aparaxial convex surface convexing toward the object side, a paraxialcurvature that is the greatest within the effective aperture, and aportion within the effective aperture that has a curvature that is lessthan ½ of the paraxial curvature, wherein said first lens group includesa positive lens element behind said negative lens element providedclosest to the object side within said first lens group, wherein theobject side surface of said positive lens element has a negativerefractive power, and wherein the following conditions (1), (2) and (3)are satisfied:R1/f<1.35  (1),D1/f>0.4  (2), and−2.5<f1/f<−1.3  (3), wherein f designates the focal length of saidimaging optical system, f1 designates the focal length of the negativelens element provided closest to the object side within said first lensgroup, R1 designates a paraxial radius of curvature of a surface on theobject side of said negative lens element provided closest to the objectside within said first lens group, D1 designates a thickness, along theoptical axis, of said negative lens element provided closest to theobject side within said first lens group.
 9. The imaging optical systemaccording to claim 8, wherein said positive lens element is a positivemeniscus lens element having a convex surface on the image side.
 10. Animaging optical system comprising a positive or negative first lensgroup, an aperture diaphragm, and a positive second lens group, in thatorder from the object side, wherein said first lens group includes anegative lens element provided closest to the object side within saidfirst lens group, wherein the negative lens element that is closest tothe object side includes an aspherical surface on the object sidethereof, said aspherical surface including a paraxial convex surfaceconvexing toward the object side, a paraxial curvature that is thegreatest within the effective aperture, and a portion within theeffective aperture that has a curvature that is less than ½ of theparaxial curvature, Wherein said positive second lens group includes acemented lens comprising a negative lens element and a positive lenselement that are cemented to each other, and wherein the followingconditions (1), (2) and (3) are satisfied:R1/f<1.35  (1),D1/f>0.4  (2), and−2.5<f1/f<−1.3  (3), and wherein f designates the focal length of saidimaging optical system, f1 designates the focal length of the negativelens element provided closest to the object side within said first lensgroup, R1 designates a paraxial radius of curvature of a surface on theobject side of said negative lens element provided closest to the objectside within said first lens group, and D1 designates a thickness, alongthe optical axis, of said negative lens element provided closest to theobject side within said first lens group.
 11. The imaging optical systemaccording to claim 10, wherein said positive second lens group furtherincludes a positive lens element on the image side of said cementedlens.